Due to the merits of high energy density, high power density, large number of charge cycles, and long storage time, power batteries (for example, lithium-ion batteries) have been widely used in portable electronic devices such as mobile phones, digital cameras, hand-held computers and etc., and also have promising applications in aspects of electricity driven transportation devices such as electric vehicles and electric bicycles, and large and medium sized electric equipment such as power storage facilities and etc. The power batteries may become the key to solve global issues such as energy crisis and environmental pollution.
When a power battery is overcharged, the electrolyte decomposition in the power battery may result in an increased pressure inside the power battery, which may cause fire and explosion of the power battery. In order to prevent the fire and explosion caused by the increased internal pressure, an external short circuit unit is generally required for the power battery. When the internal pressure of the power battery increases, the external short circuit unit may generate a short circuit between positive and negative electrode plates of a bare cell and an outer portion of the power battery, and thus the charging of the bare cell may be suppressed.
However, the above structure would reduce the performance of the power battery under high-temperature environment. For example, when doing a Hot-Box test with the above structure, a probability of thermal runaway for the power battery may largely increase. The specific reason may be: under high-temperature environment, not only the internal pressure of the power battery increases with the electrolyte decomposition under high-temperature, but also an internal impedance of the bare cell increases. In this case, if a turnable plate is reversed such that the positive electrode plate and the negative electrode plate of the power battery form an external short circuit, more heat will be generated within the bare cell because of the increased internal impedance and short-circuit current, which may further intensify the risk of fire and explosion of the power battery. In other words, the external short circuit unit may solve only the overcharge problem of the power battery under normal temperature, but would increase the thermal runaway probability of the power battery in high-temperature environment.